1. Field of the Invention
The present invention generally relates to optical filters, and more particularly to a technique for tuning a dielectric filter in a collimator assembly.
2. Technical Background
Data communication systems increasingly are employing light signals and optical fibers for the transmission of information. The use of optical fibers allows the transmission of large amounts of data at high speeds and with low signal loss over long distances. To increase the data transmission capacity on an optical fiber, a plurality of light signals at different wavelengths are commonly multiplexed with wavelength division multiplexing for transmission through a single optical fiber so that the information is transmitted on multiple wavelengths, i.e., channels. In a wavelength division multiplexed system, the plurality of light signal sources have different wavelengths corresponding to different signal channels. After the multiple channels are transmitted through the optical fiber, the multiple wavelength signals are separated at a receiving end with the use of a demultiplexer to separate the individual signal channels. Select wavelength band filters may be used as one technique to select specific channel wavelengths.
In order to maximize utilization of the available bandwidth, the channel wavelength band and any wavelength separation between adjacent channels should be minimized. Accordingly, to minimize the wavelength band for each signal channel, a narrow band filter is used for accurately selecting the narrow band channel. Such filters are generally fixed, although other filters are tunable to a selected frequency.
One common filter tuning approach is to tune a dielectric filter in a collimator package to resolve a single spectral feature, such as a peak value. The single spectral feature is generally correlated to a specified waveform and serves as the target wavelength for resolving the angle of incidence for that filter. One disadvantage to this approach is that the accuracy for resolving the target wavelength based on a single spectral feature is generally limited such that the per channel wavelength band of the filter is limited. Inaccuracy in resolving the target wavelength may induce significant error for optimal spectral alignment of the dielectric filter. Accordingly, the accuracy of the dielectric filter's initial spectral measurement and optimizing the resulting target wavelength currently limits precise spectral alignment to a collimator assembly's optical axis. For this reason and others, it is desirable to provide a technique and structure for tuning a tunable filter with a high degree of accuracy.